In certain mobile radio systems, a plurality of fixed radio stations or base stations share a common radio channel called a time-shared control channel, and transmit sequentially on this channel. This type of system is used when there is a lack of radio channels, and the traffic density is low. In such mobile radio systems, each mobile radio responds only to the control signal burst transmitted on the time-shared control channel by the base station to which the mobile radio is currently registered, and signals back to the system (to the exchange) only via this particular base station during the reception of the control signal burst. However, if the control signal of the base station is no longer of sufficient level when received at the mobile radio, the mobile radio selects a new base station on the basis of the control signal levels received from the other base stations, and registers to the selected base station. In this type of system, the utilization of a time-shared control channel unavoidably leads to a situation where the time required to set up calls between the mobile radios and the network is statistically longer than in a system in which each base station has a dedicated control channel (which is not time-shared). This is because the base station may have more messages to be transmitted and received than what it is capable of handling during its transmission time slots on the time-shared control channel.